Catalytic properties of a highly thermoactive polygalacturonase from the mesophilic fungus Penicillium occitanis and use in juice clarification

• A novel polygalacturonase (PG1) is purified from the fungus Penicillium occitanis.
• PG1 is highly thermoactive with maximal enzymatic activity at 70 °C.
• The specific activity toward PGA is amongst the highest fungal ones.
• The PG1 showed an endo-polygalacturonase behavior.
• The purified PG1 enhanced the yield of juice extracted from citrus.

A new polygalacturonase (PG1) is purified to homogeneity from the hyper-pectinolytic mutant (CT1) of Penicillium occitanis by using two chromatographic steps. The purified PG1 exhibited a very high specific activity toward PGA, namely 57533.2 U/mg of protein and a high optimal temperature, 70 °C. In our knowledge, it is one of the highest temperature optima described till now, even among those reported for thermophilic fungi; recalling here that our fungus is a mesophilic one. The N-terminal sequence was almost identical to that deduced from the previously cloned pga1 gene. The mass spectrometry analysis of PG1 further confirmed its belonging to the pga1 gene. As the peptide sequence of the pga1 bears the signature of endopolygalacturonases, we brought in this work evidences that it belongs to enzymes that hydrolyze pectin by endo-fashion. Indeed, during the hydrolysis of polygalacturonic acid by PG1, the viscosity drops very quickly while reducing sugars were released very slowly. In addition, thin layer chromatography showed that mainly oligosaccharides were released from PGA, namely tetra and tri-galacturonic acids. The purified PG1 was able to enhance the clarification of citrus juice. Considering all these properties, this novel fungal would be an interesting biocatalyst for future application in fruit and vegetable transformation.

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